experimental and theoretical studies of the magnetocaloric effect (mce) in the mn 5-x fe x si 3...
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Experimental and theoretical Studies of the Magnetocaloric Effect (MCE) in the
Mn5-xFexSi3 Series
Michael Gottschlich1
Olivier Gourdon1, Michael Ohl1, Jörg Perßon2
1 Jülich Centre for Neutron Science outstation at the SNS at ORNL
2 Peter Grünberg Institut Forschungszentrum Jülich
The MCE
f
i
f
i
H
HHH
ad
H
HH
M
dHT
M
C
TT
dHT
MS
0
0
MCE of Gd, Gschneider, et al. 2005
The MCE is related mostly to the magnetic entropy changes of magnetic materials under the influence of an applied field
Tc where the phenomenon occursS –MCE obtains T of the MCE phenomenon
0, ElLatMagadiabaticTot SSSS
Application of the MCE
B = 0
T=T1
Application of the MCE
B > 0
T>T1
Application of the MCE
B > 0
T=T1
Application of the MCE
B = 0
T<T1
Fe(ab) 0 ~1/4 1/4
Fe(c) 1/3 2/3 0
Si ~3/5 0 1/4
Hexagonal P63/mcm
a = b ~ 6.8 Å
c ~ 4.7 Å
Fe(ab) Fe(c)
Si
Unit cell of Mn5-xFexSi3 at room temperature
Fe(ab) 0 ~1/4 1/4
Fe(c) 1/3 2/3 0
Si ~3/5 0 1/4
Hexagonal P63/mcm
a = b ~ 6.8 Å
c ~ 4.7 Å
Fe(ab) Fe(c)
Si
low cost
non-toxic
Unit cell of Mn5-xFexSi3 at room temperature
Unit cell of Mn5-xFexSi3 at room temperature
Fe(ab) 0 ~1/4 1/4
Fe(c) 1/3 2/3 0
Si ~3/5 0 1/4
Hexagonal P63/mcm
a = b ~ 6.8 Å
c ~ 4.7 Å
Fe(ab) Fe(c)
Si
low cost
non-toxic
structure flexible/ accommo-date various chemical substitutions
understanding how the MCE works
Synthesis: Mn5-xFexSi3 (x=0,1,2,3,4)• polycrystalline samples prepared by inductive crucible free melting
• structures preliminary confirmed by x-ray diffraction
• magnetization measurements
• chemical Analysis
MCE in Mn5-xFexSi3
Songlin et al. 2002 Recently at ORNL (X=4)
MCE of Gd5Ge2Si2 (2T)~27 J/kg K
E. Brück et al. 2007
TOF instrument (ideal for atomic occupation / high Q)
high resolution:Δd/d ~0.1%
Neutron the rescue… to elucidate the coloring problem: Fe vs. Mn on both sites (no discernable by X-ray) to investigate the magnetic ordering
…POWGEN at the SNS
Schematic view of POWGEN
80000
60000
40000
20000
0 0 0.5 1.0
d [Å]
Inte
nsi
ty
Diamond pattern collected on POWGEN
“unique precision”
X theor % Fe(c) 1 % Fe(ab) x calcul0 0 0 01 0.440 0.038 0.99752 0.754 0.161 1.9933 0.923 0.389 3.01684 0.988 0.673 3.99845 1 1 5
No
rmal
ized
Inte
nsi
ty
Mn5-xFexSi3 (x= 0 to 4)
Fe(ab)
Fe(c)
Si
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
No
rmal
ized
Inte
nsi
ty
0.5 1.0 1.5 2.0 2.5 3.0 3.5
d [Å]
300 K
x=2
Mn5-xFexSi3 (x= 0 to 4)
Candini et al. 2004
Very similar results.
300 K
Our data from SNS
Magnetization Measurements
best MCE candidate
Magnetization Measurements
Moments II c-axis for x=4 in the ferromagnetic phase
LT structure of Mn5-xFexSi3 x=4
Fe(ab)
Fe(c)
Si10K
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
No
rmal
ized
Inte
nsi
ty
0.5 1.0 1.5 2.0 2.5 3.0 3.5
d [Å]
300K
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
No
rmal
ized
Inte
nsi
ty
0.5 1.0 1.5 2.0 2.5 3.0 3.5
d [Å]
P63/mc‘m‘
DFT Calculationsusing program „TB-LMTO-ASA“, R. Tank et al.=> occupations of Mn vs. Fe=> stability of the AF and F phases
Name wyck x y z ___________________M1 2i 0.3333 0.6667 0.0000M2 2i 0.6667 0.3333 0.5000M3 2i 0.7636 0.7636 0.2500M4 2i 0.2364 0.0000 0.2500M5 2i 0.0000 0.2364 0.2500Si1 2i 0.4043 0.4043 0.2500Si2 2i 0.5957 0.0000 0.2500Si3 2i 0.0000 0.5957 0.2500
X=4From group to sub-group
P63/mcm P-1
1Mn for 4Fe
Model 1Mn on Fe(c)
Model 2Mn on Fe(ab)
Fe(ab)
Fe(c)
Si
DFT CalculationsLDA and LSDA calculations have been performed both confirmed that:
Model 1Mn on Fe(c)
Model 2Mn on Fe(ab)is less stable than
by 0.5 eV/unit cell
in agreement with the refined data
magnetic moments of ~1.7 B small magnetization on Si ~0.1B (indirect effect)
Total Density of States
Mn5-xFexSi3 x=0
Negative MCE occurs here
Mn5-xFexSi3 x=0
Mn5-xFexSi3 x=0
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
No
rmal
ized
Inte
nsi
ty
0.5 1.0 1.5 2.0 2.5 3.0 3.5
d [Å]
85 K
AF2 structure
orthorhombic
Mn5-xFexSi3 x=0
Space Group P21/m
a 6.88357(3) Å
b 4.81331(2) Å
c 6.9046(1) Å
β 119.897(2)°
No
rmal
ized
Inte
nsi
ty
d [Å]
60 K
AF1 structure
monoclinic
Acknowledgements
POWGEN at SNS ORNL
Jason Hodges
Ashfia Huq
HB2a at HFIR ORNL
Ovidiu Garlea
Clarina Dela Cruz
JANA Software Vaclav Petricek
Summary and future directionthe combination of experimental data and theoretical tools lead to a better understanding of the MCE property.chemical substitutionssingle crystals for further neutron scattering experiments
Thank you very much for your attention!